The present invention relates generally to arrowheads for archery arrows and, more particularly, to a uniquely configured broadhead having a relatively long monolithic solid ferrule and a high strength, rear entry blade mounting system with the blades having a complex cutting edge geometry for effective harvesting of game. The ferrule and the blades are manufactured using metal injection molding (“MIM”) and/or liquid metal molding (“LMM”). The present invention further relates to defining and applying a superior MIM process. In addition, the present invention relates to a field point having a mass and center of gravity that is substantially equivalent to the broadhead for accurate tuning of an archery bow from which the broadhead may be shot.
Archery broadheads with fixed or replaceable blades are well known in the art. Such broadheads are deployed on the end of an arrow and may be adapted to be removable from the arrow. The broadhead itself typically comprises a body or ferrule into which blade members may be inserted such that the blade members may be replaced or sharpened. Generally two types of replacement blade broadheads exist; broadheads with front loading blade systems and broadheads with rear loading blade systems. The front entry blade systems are characterized by broadheads that secure the blade with a screw-on or screw-in tip which is threadedly attached to the broadhead ferrule. The blades are inserted from the tip end which is the end farthest from the arrow.
The rear entry broadhead is characterized by the blades entering the ferrule blade grooves from the threaded shank end of the broadhead ferrule which is the end closest to the arrow. The rear entry replacement blade broadhead secures the blades by a washer which is compressed to the arrow using the torque provided by the arrow or by a threaded-on nut which connects to the broadhead ferrule on the threaded shank. Typically rear entry replacement blade broadhead ferrules are more robust compared to front loading broadhead ferrules. In addition, only rear entry replacement blade broadheads can offer a monolithic solid ferrule.
When offered in any of the high strength materials like stainless steel or titanium, the rear entry monolithic ferrule yields the best overall strength and robustness characteristics. Unfortunately, many broadheads of the prior art suffer from several deficiencies that detract from their overall utility. For example, in many prior art broadheads, the connection of the blade members to the ferrule is relatively weak causing the ferrule or blade member to become damaged upon impact with relatively hard bones of large game. In addition, the ferrule may become damaged upon impact with other hard surfaces such as rocks that are hit during missed shots.
U.S. Pat. No. 5,160,148 issued to Musacchia discloses a broadhead having a front loading ferrule with axial passageways and slots extending through the length of the ferrule. Blades are secured to the ferrule by sliding the blades from the front or tip end into the slots. A tip member is threaded onto a leading edge of the ferrule to capture the blades within the slots. Although the broadhead as disclosed in the Musacchia reference provides a relatively simple means for blade removal, the axial passageways and slots in the ferrule may greatly weaken the ferrule such that impact with relatively hard surfaces such as bone or rocks may cause the ferrule to bend or shatter and may also result in shearing off, shattering, or splitting of the threaded-on tip.
U.S. Pat. No. 6,595,881 issued to Grace describe a powder injection molded fixed blade broadhead where the broadhead blades are secured by a threadedly secured tip. No claims are made regarding this fixed blade broadhead but several conclusions can be taken from the drawings of Grace. Broadheads with threadedly attached tips are prone to misalignment which can cause arrows to veer off course. The ferrule has a triangular cross section and the blades are secured into T-shaped blade slots and inserted from the threaded tip end. The T-shaped slots are shown to have constant width and the T-shaped base is also of constant width. Because Grace is understood to disclose that the as-molded T-shaped blade slots lack draft, it is believed that the ferrule cannot be effectively molded.
At best, the ferrule will experience distortion and the mold itself will experience premature wear on the T-shaped mold inserts. Furthermore, the base of the T-shaped blade slot base has sharp right angled inside corners which generate stress risers in the molded part and can lead to molded part distortions and failure. The ferrule taper is shown as linear with the widest outside diameter towards the rear or mating end. A tapered or linear tapered ferrule starting from the mating end to the screw in tip as shown by Grace is heavier than a ferrule which has a non-linear tapered ferrule or which has a surface which has multiple stepped tapers. The ideal ferrule cross-section would be nearly constant over much of the ferrule length which would allow for sufficient length and strength around the blade grooves. In addition, the tapered triangular ferrule of Grace must be shortened in order to meet the specified weight which is an undesirable feature.
U.S. Pat. No. 5,160,148 issued to Musacchia clearly shows a relatively long non-linear tapered ferrule. The Musacchia ferrule is disclosed as having two different tapers or stepped tapers. U.S. Pat. No. 4,529,208 issued to Simo shows a varying shaped cross-section which extends the length of the ferrule. The Grace ferrule with the same maximum diameter base section, which mates with the arrow, will be heavier when compared to the Musacchia and Simo ferrules of equal length and maximum base diameter. For this reason, the Grace ferrule must be shortened in order to meet a given design weight such as 125 grains. Reducing the overall ferrule length is undesirable as it causes the blade to have a steep angle which increases blade stress and can reduce penetration.
In addition, the cutting diameter of the broadhead may need to be reduced because of the shortened ferrule length which can reduce wound channels which, in turn, reduces the effectiveness of harvesting game humanely. The threadedly secured tip is relatively weak when compared to a tip of equal or less diameter that is machined or molded on a monolithic solid ferrule. The triangular cross section of the Grace ferrule causes undesirable thin wall molding conditions, especially considering that the outside surface is slightly concave as shown between the inner T-slots and the outside surface of the ferrule which can result in a weak ferrule. Since the triangular ferrule tapers with the smallest portion towards the tip, the wall thickness between the T-shaped slot and the outer surface is thinnest at the tip end. The T-shaped slots of Grace are disclosed as being molded but no taper or draft is shown or discussed.
Because the threadedly secured tip is shown to thread into the broadhead ferrule, sufficient wall thickness must occur between the tip's threaded post and the T-shaped slots. The combination of providing sufficient wall thickness between the wide T-shaped slot and the outer concave triangular ferrule surface, and providing adequate thickness between the threaded tip aperture and the T-shaped slot with the widest section of the T-shaped slot at the tip, and combining with a tip post diameter of sufficient strength to withstand high impact, all result in a ferrule tip which is large in diameter when compared to the tip diameter of a rear entry monolithic ferrule.
A large diameter tip is heavier than a smaller diameter tip and as such the broadhead must be shortened to achieve the typical specified weight. This reduced length causes the broadhead blade to be shorter which results in a steep blade angle and possibly a smaller cutting diameter such that the effectiveness of generating wound channels may be compromised. In addition the T-shaped slots with their widest section towards the tip, limits the overall length of a broadhead. Any attempt to seat the blades deeper towards the longitudinal axis, which could allow for a longer ferrule, is negated due to the threaded-in tip and its requirement to be of large enough diameter to be substantially strong. If the tip is broken the blades are no longer secured and are free to be displaced or fall out of the ferrule. The broadhead can no longer take game humanely.
In Grace, the blades are shown to be triangularly shaped which can cause unpredictable flight and wind planing which results in the broadhead veering off target. Grace shows a T-shaped blade base which does not taper in width which is otherwise desirable in a molded part. Furthermore, the T-shaped blade base is shown to have sharp right angles on all corners which provide stress risers in molded parts and increase the possibility of molding, debinding, and sintering distortions.
Grace discloses a preferred embodiment wherein the blades are releasably secured to ferrule near the tip. However, one skilled in the art will recognize that the ferrule could be configured such that a releasing element disposed over shank or arrow shaft functions to releasably secure the blades to the ferrule. A solution to the above-described deficiencies of the Grace tip is not obvious. A completely different arrow securing design or rear entry broadhead is even less obvious. A need exits for a robust replacement blade broadhead of sufficient length and cross section so as to offer a superior blade retention system.
U.S. Pat. No. 4,146,226 issued to Sorensen discloses an arrowhead having a plurality of longitudinal slots formed about a body of the arrowhead with a dovetail angle formed at an intermediate location in the body along each one of the slots. A removable blade may be secured to the body by means of an extension that is inserted into a receiving recess in the body. A conical nose member is installed on a front end of the body. Although the arrowhead of the Sorensen reference allows for blade removal for replacement or sharpening thereof, the dovetail slot weakens the ferrule such that the ferrule may shatter upon impact with a hard surface and the separate removable tip is prone to misalignment with the ferrule.
Another deficiency associated with broadheads of the prior art is ineffective blade design. Ideally, blade members of a broadhead are designed such that the broadhead will easily penetrate the hide of an animal and generate extensive internal wound channels in order to cause the animal to swiftly and humanely expire. In addition, the blade members of a broadhead are ideally configured so as to enhance the accuracy of the flight pattern of the arrow.
Unfortunately, in prior art broadheads, the use of large blade members for generating extensive wound channels has an adverse effect on flight characteristics due to wind planing (veering off course) of the arrow due to the large blade size. Conversely, the use of small blades, while increasing the flight accuracy, results in ineffectiveness of the blade in generating wound channels. The prior art includes several broadhead configurations that attempt to reconcile these opposing characteristics.
For example, U.S. Pat. No. 4,505,482 issued to Martin discloses a broadhead having a ferrule with symmetrically mounted blades. An outer edge of each one of the blades slopes toward the other blades at a shallow angle to form a needle-like point. At a rear portion of each one of the blades is a vent opening which purportedly reduces noise generated by the arrow during flight. Such noise is undesirable in bow hunting as the noise may startle the game when the arrow is shot. Unfortunately, such vent openings of the Martin reference are understood to increase noise and impede penetration of the arrow into the animal such that the effectiveness in reducing noise and generating wound channels may be compromised.
U.S. Pat. No. 5,044,640 issued to DelMonte et al. discloses a broadhead having a plurality of blades spaced about a conical tip shaft. Each one of the blades is shown and illustrated with a generally large radius. The broadhead includes a ring blade having a diameter larger than that of the arrow upon which the broadhead is mounted such that when the arrow is shot from a bow, the ring blade will cut a hole that is greater than the shaft diameter. In this manner, the arrow shaft cannot plug the entrance wound made by the broadhead such that the animal may more quickly expire from blood loss. Although the broadhead of the DelMonte reference may facilitate blood loss, the generally small radius of the blades is understood to minimize the ability to generate extensive wound channels and the ring blade reduces penetration.
Another deficiency associated with removable broadheads of the prior art is relative movement between the broadhead and the arrow shaft. As was earlier mentioned, accuracy in the flight of the arrow is critical in bow hunting for obvious reasons. However, prior art broadheads that are removably mounted on an arrow may become loosened while the arrow is resting in the bow quiver resulting in relative movement between the broadhead and the arrow. In addition to causing a rattling noise while stalking game which may scare the game away, such relative looseness may also result in misalignment between the broadhead and the arrow which may cause the arrow to porpoise, fishtail or otherwise veer from its flight pattern. Furthermore, such relative looseness may allow moisture to enter the gap between the broadhead and the arrow resulting in corrosion of metallic mating surfaces of the broadhead and arrow shaft. Over time, the looseness may eventually result in loss of the broadhead while being carried in the bow quiver.
U.S. Pat. No. 6,595,881 issued to Grace tries to address the problem of broadheads loosening on the arrow shaft by deploying a compliant member interposed between said ferrule and said arrow shaft. This technique compresses the compliant member between the ferrule and the shaft. Over time this technique actually can create a loose broadhead. Compliant materials such as Teflon, rubber, and silicon are materials which will permanently deform, cold-flow, and extrude while under intense pressure as is the case when you tighten the broadhead ferrule to the face of the arrow insert. Once the compliant member deforms the broadhead will loosen. Furthermore when the compliant member is deployed between the base of the broadhead ferrule and the face of the arrow insert, it can cause misalignment between the broadhead and the arrow shaft. A need exits for a device to prevent a broadhead or field point from prematurely loosening from the arrow shaft and to center the broadhead or field point within the arrow shaft.
Another deficiency of broadheads of the prior art concerns the tuning of the bow from which the arrow is to be shot. As was earlier mentioned above, accuracy of the flight pattern of the arrow is critical in bow hunting for obvious reasons. Archers typically tune their bows using field points instead of the broadhead so that the sharpened edges of the broadhead do not become nicked or damaged. Field points generally lack the blades used in broadheads as the field point is only used to target practice, to tune the bow, and to check and align the point of aim of the bow. However, in order to accurately tune the bow such that the broadhead will fly similarly to the field point, the field point must have the same length, mass and balance point as the broadhead and must be durable to withstand repeated use on targets which may have broken arrows and points imbedded in the practice target.
For example, if the broadhead has a mass of 125 grains and a given center of gravity, the field point should likewise have a mass of 125 grains and a center of gravity in the same location as that of the broadhead and be of the same length as the broadhead. Unfortunately, unless a field point is specifically manufactured to match the mass and balance point of a given broadhead, it is difficult to accurately tune the bow. In addition, because field points lack blades which may be used to tightly thread the field point into the arrow, the field point may not be tightly secured to the arrow such that, over time, relative looseness may develop between the field point and the arrow which can reduce bow tuning accuracy as well as lead to a loss of the field point. Glue, wax, epoxy and the like is sometimes used by archers to rigidly secure the field point to the arrow. However, such techniques are messy and time consuming.
U.S. Pat. No. 6,027,421 issued to Adams discloses a tuning point for archery. This tuning point is defined as having a separate tip, body and weight ring. This tuning point is further defined by the tip and weight ring as being steel and the body is aluminum. Tuning tips of this design are prone to loosening from the arrow insert causing noise and causing an overall distraction while practicing archery. Tuning points of this design are weaker when compared to monolithic solid tuning points. The separate tip is prone to misalignment with the arrow shaft and may shear off when impacting with a hard object. The relatively long aluminum body may lack straightness. New families of compact, short broadheads exist, and these heads have balance points which are closer to the arrow. Since these heads are shorter they require a balance point closer to the arrow and have the overall length shorter. A need exits for a monolithic solid tuning point which has a balance point which closely matches relatively short broadheads and a need exits for a tuning point that will not prematurely loosen from the arrow shaft.
U.S. Pat. No. 5,114,156 issued to Saunders discloses an arrow point which threadedly attaches to an arrow insert within the practice arrow. This arrow point is prone to vibrate loose and cause noise and unwanted distraction while practicing archery. Archers apply several techniques to prevent arrow points of this design from vibrating loose. These include applying glue, epoxy, and wax to the threaded end of the arrow point which prevent the arrow point from loosening. These applications to the threaded connection may foul the insert and may require the arrow inserts replacement if the arrow point is to be exchanged for a different arrow point. There is a need for a practice field point that does not vibrate loose or prematurely loosen from the arrow shaft.
Regarding deficiencies of the prior art associated with manufacturing of broadheads, U.S. Pat. No. 6,290,903 issued to Grace discusses the method of manufacture of broadheads using a powder injection molding (“PIM”) process. Grace describes the PIM process as: 1. Premixing metal powder with binder in a first blending step; 2. Fully mixing powdered metal and binder into a nearly homogeneous mixture; 3. The homogenous mixture is pelletized in a second blending step; 4. The powdered metal composition is injected into a broadhead mold; 5. The molded greenware broadhead is processed to remove the binder, by the preferred process of immersing the broadhead in a solvent; 6. In a second debinding process, the partially debound broadhead is placed in a thermal debinding furnace where any remaining binder is burned off and if required this furnace can perform a pre-sintering step; 7. The powdered metal broadhead is placed in a sintering furnace and sintered at an elevated temperature and at an elevated pressure to increase density. Once sintering is complete the broadhead is in its final shape and includes its molded features.
Grace discloses that though solvent debinding is preferred, one skilled in the art will readily recognize that any process or combination of processes could be employed to debind the greenware broadhead. However, it is believed that debinding processes are uniquely suited to a specific PIM process. More specifically, it is believed that the PIM process as a whole is a dependent process where each of the processing steps is dependent on the other processing steps. A change in the debinding process requires a change in the binder or raw material which dictates the injection molding parameters, and changes the sintering process up to and including requiring a completely different type of sintering furnace.
Grace begins with premixing metal power and binder but skips several steps in the process. In the PIM process both the metal powder and binder must be procured separately. The binder and the metal powder must be certified as to meeting specified criteria. After mixing and before pelletizing, the mixture must be checked to make sure it is indeed homogeneous. Uneven distribution of the powder in the binder will result in the loss of dimensional control and cause variations in part density. Variations in the feedstock consistency from batch to batch will also result in a loss of part dimensional control. Following pelletizing, the pellets must be checked for proper performance and suitability for molding.
Consistent granule feedstock is a requirement to obtain consistent molded parts. The injection mold must be scaled up in size to match the binder system used. Various binder systems require the mold to be scaled up from 17% to 21% and this is determined by the binder and base metal material. If the chosen binder is intended for solvent debinding, it will have a different scale-up percentage when compared to a binder designed for catalytic debinding. If a part is molded in a mold designed for a 21% part scale-up with a feedstock which actually requires a 17% scale-up, then the molded part will weigh more and be oversized. Because broadheads are measured in grains where 7000 grains is equivalent to an English pound, a 125 grain broadhead requires precise dimensional control because precise part weight (i.e., precise broadhead mass) is required. A broadhead weighing more than five (5) grains over or under weight when molded with different binder systems is Unacceptable.
Once the injection mold is in place in the injection molding machine, the part may be molded and is then ready for debinding. Suitable binders for solvent debinding can often exhibit weak greenware strength and care must be taken to prevent damage to the part prior to and during solvent debinding. The solvent debinding process is very slow and it is the gating item in the PIM process. Furthermore, the solvent debinding process eliminates the likelihood of having a continuous process. Solvent debinding is processed at relatively high temperatures and part distortion is possible and temperature control and uniformity are critical.
Injection molding is believed to outpace solvent debinding on large part runs which necessitates that parts must be stored in a holding process prior to debinding. This unfinished inventory has a negative affect with turning the unfinished inventory into revenue. Once solvent debinding is complete the parts are then transferred to thermal debinding. Finally the parts are sintered at high temperature and at high pressure. The requirement to have two debinding steps is slow and requires added capital expense. The requirement to sinter parts at high pressure means that an oven must be opened, parts to be sintered must be loaded and, of course, the furnace must be closed, all of which can increase the risk of part damage, contamination and furnace seal failure.
Thus, there is a need for a standard ambient pressure or slightly negative pressure sintering furnace which is ideal for continuous production. High pressure ovens as described by Grace are prone to leak and difficult or impossible to run a belt conveyor through which is typical of continuous processes. It is believed that the Grace process lacks the ability to readily automate the manufacturing of broadheads and make it continuous and is largely batch oriented starting from the requirement to procure and mix, and compound two different materials. Finally the chemicals used in chemical debinding can be caustic, damaging to the ozone layer, and expensive to dispose of and they include substances like chlorine and heptane.
An alternative debinding system is neither obvious nor interchangeable as Grace discloses. The PIM process as disclosed in Grace is not understood to be capable of filling the need for a system which can be run in a continuous fashion wherein the process requires no mixing of components and thus allows for streamlining of the quality and procurement process. Removing component mixing as a process step creates the desired need to purchase ready made, certified, granulized molding feedstocks that can be fed directly into the injection molding machine without verifying component makeup or homogeneity of granule feedstock received from the supplier and furthermore increases the overall quality of the process by removing batch to batch component mixing variances.
A need therefore exists to reduce the capital cost of PIM systems by eliminating the need to purchase mixing and pelletizing equipment and return the focus of a molding facility back on its core business, injection molding. There is also a need to eliminate potentially caustic and dangerous solvent debinding systems and remove any requirement to process, remove or dispose of any debinding bi-products. In addition, a need exits to debind at a rate of 10 to 40 times faster than solvent debinding in order to enable continuous production. There is a need to eliminate at least one debinding process such as thermal debinding. There is a need for a part, as a result of molding with a pre-made granular feedstock, which exhibits tremendous greenware strength for easy handling and ease of debinding.
A need therefore exists for a metal injection molding (“MIM”) system that, as a result of the above requirements, delivers very cost effective parts with the ability to lower part costs due to continuous production. The Grace process is understood to disclose a minimum of seven (7) process steps. There is a need for a MIM process with only three (3) process steps. The Grace process requires mixing/blending and pelletizing equipment. The Grace process requires two furnaces, a debinding furnace and a high pressure sintering furnace. These repeated process steps need to be eliminated.
There is a need to reduce the capital equipment costs, reduce the process steps and increase production as defined by the Grace powder injection molding process. The solutions to these market and process needs associated with PIM are not obvious. There is a need for a MIM process which uses commercially available feedstock. This MIM process must have the capability to run as a batch process and also a high volume continuous process and must eliminate mixing and pelletizing of components. There is a need for a MIM process which creates no harmful bi-products or any bi-product requiring waste removal. There is a need for an MIM process that greatly reduces the number of process steps as required by the prior art PIM process.
In light of the above discussion, there exists a need in the art for a broadhead having blade members-that are joined to the ferrule in a relatively strong manner such that the ferrule or blade member will not be damaged during use. In addition, there exists a need in the art for a broadhead having a blade design that allows for stable and accurate flight of the arrow without wind planing. There also exists a need in the art for a broadhead having a blade design that will easily penetrate the hide of an animal and generate extensive internal wound channels.
Furthermore, there exists a need in the art for a broadhead that may be removably secured on an arrow with minimal relative movement therebetween so as to improve the accuracy of the flight of the arrow and to prevent loss of the broadhead. There also exists a need in the art for a broadhead that is easy and safe to assemble and disassemble. Finally, there exists a need in the art for a field point having physical properties (i.e. mass and balance point and length) that match a given broadhead to allow for accurate bow tuning. A need exists for a field point which offers a high strength construction. There exists a need in the art for a field point which remains tight to the arrow shaft and remains quiet in flight. There exists a need in the art for a tuning point of monolithic construction that matches the length and balance point of relatively short broadheads.